That's high. Any trouble planing?

That isn't high with a notch or box. If he can get on plane with the bravo without too much problem than that is the prop he should run. I agree the heads and exhaust are the problem. How about some anodized aluminum heads. I lean toward AFR and Lightning headers.

I run in salt also and went with EQ heads. The are rumored to be the old RHS castings. Not overly well known yet but the people running them have been very happy. Between boat guys and car guys they really like the heads. Dollar for dollar likely the best head on the market. I bought mine bare for like $435 each. They are at the machine shop right now getting cleaned up and ready to go. The model to check out is ch-454-a

even down on power if the boat is running anything over 40 mph the water should not be coming off the notch at a 45 degree angle. that boat with a 525 runs cleaner than that. something else is wrong with the setup or the way he is trimming the drive or the weight distribution or the bottom.

Without pics of what he means it's tough to say how the water is coming off the notch. In theory on an integrated swim platform it would be nearly impossible to see the water coming off a notch. He's not as fast as he things he should be is the main issue and it's likely because he isn't quite making the power he thinks.

24. Bravo 1 4k 52 mph 14 %
26 bravo 1 4k 56 mph 8 %

Do slip at wot. You'll generally have more at cruise due to the fact more hull is wet and therefore more drag.

24 at 5500 73 12%
26 at 5100 70 at 16%

The bottom line is that I am loosing about 75 hp from the exhaust system and once the motor is mounted in the boat

12% is a good number. You're right the exhaust is limiting you. Like I said I'm in the same situation. Contemplating ditching the exhaust before I even dyno. Lol